This spin-1/2 particle which behaves in a quantum manner could be the
fundamental building block of a Quantum computer. We could call it a
qubit, to denote that it is analogous in some ways to a bit in a
classical computer. Just as a memory register in a classical computer
is an array of bits, a quantum memory register is composed of several
spin-1/2 particles, or qubits. There is no particular need for the
spin-1/2 particle, we could equally well use a Hydrogen atom, and
designate its electron being measured in the ground state to be the 0
state, and it being in the first excited state to be the 1 state.
There are a multitude of possible qubit representations that will
work. For simplicity only the spin-1/2 particle will be discussed from
here on.